This invention concerns a method for the storage and controlled supply of electric energy for discontinuous loads in steelworks.
To be more exact, the method according to the invention provides for the reduction of power peaks absorbed from the electrical supply network according to the highly variable conditions of load and of working of the devices functioning in the steelworks, especially as regards electric furnaces and rolling mills.
One of the most important problems encountered in steelworks relates to the supply of electric energy by the supplying Authority.
It is known that the very high power required for the working of the various devices is faced with the limited power of the electricity lines and with the Authority's requirement to have a constant load in those lines.
This entails for the steelworks the burden of particularly harsh contracts, since electric furnaces in particular have in their various working steps very variable conditions of load requiring peaks of active power much higher than the mean absorbed power.
In fact, the typical working cycle of electric furnaces is characterised by a considerable variability and discontinuity of the value of the absorbed electrical power.
A steel melting furnace changes typically from a maximum value of absorbed power, when it is engaged in the melting step, to a substantially zero absorption during the step of tapping and of charging scrap.
In some intermediate working steps, such as perforation for instance, the furnace has a given absorption which is less than the maximum value.
The inclusion of a ladle furnace for secondary metallurgy, even if it requires power much less than that required by a melting furnace, contributes to the worsening of the situation inasmuch as the ladle furnace absorbs the maximum power for a shorter period than the cycle of the melting furnace.
Where there are common rolling mills for the production of strip and wide flats, it is known that the slab leaving the continuous casting plant is generally sheared to size in segments which are then sent to the rolling mill stands.
This method entails very high peaks of power when the rolling mill stands start working, these peaks lasting for a very short time; this involves the installation of electric lines able to withstand these peaks.
So as to avoid this problem, all steelworks normally employ the technique of restricting costs by using a lower power than that required and install plant to measure and predict the energy consumption during the period required by the supplying Authority to provide the higher power.
If the consumption of energy in that period exceeds the foreseen consumption, the load is reduced by stopping the electric furnace, rolling mill or usage means involved at that moment. This is an especially damaging shortcoming for the ideal working of the plant.